A senior police commander said an explosion that injured at least 20 people at a public hospital on Monday morning was caused by a bomb.

The explosion struck a reception room for retired civil servants at the Phramongkutklao Hospital at about 11am on Monday, the same day Thailand marked the anniversary of a coup d’etat that brought the current military regime to power three years ago. Deputy police commissioner Srivara Ransibrahmanakul said evidence of a bomb was found at the scene.

“It’s confirmed to be a bomb,” Gen. Srivara told reporters. “We must convene a meeting before saying anything further, but at this time, I can confirm it was a bomb.”

Traces of battery and electrical wires were found, the deputy police chief said.

Rescue workers said at least 20 people were wounded at the hospital which is on Ratchawithi Road near the Victory Monument.

Col. Preecha Saomuang of Phaya Thai Police said soldiers have sealed off the crime scene, and police officers are not allowed into the area.

Monday’s incident coincided with the third anniversary of the 2014 military takeover. It comes just a week after a small bomb wounded two people in front of the National Theatre in Bangkok’s historic quarter.

You want to protest the Juntas rule--so you set off a bomb in a hospital waiting room -- I don't understand the relevance or symbolism.

It was an army hospital. It sends a message that they, the bombers, are able and are prepared to attack anywhere. Although in view of the fact the CCTV allegedly wasn't working, it does rather raise question marks as to who was behind it? Same as the 11 CCTV cameras by the democracy memorial that recently disappeared.

BANGKOK – A man arrested over the bombing of an army hospital in Bangkok said Tuesday that he carried out the attack that wounded 21 people as an act of resistance against Thailand's ruling military junta, his criticisms of the government overshadowing police pride in solving the case.

Wattana Pumret, a 61-year-old retired electrical engineer for a state enterprise, said at a police news conference that he acted on his own when he planted a bomb in a guest reception room in Phramongkutklao Hospital on May 22, the third anniversary of a military coup that ousted a democratically elected government.

In front of senior police officials, he said calmly that he carried out the bombing as a "symbol of defiance" against Thailand's military government.

"I do not hate the army, I love the army. But I hate some soldiers who use the people as a stepping-stone to gain power and become prime minister and the government," said Wattana, who was allowed to answer questions.

Police said they have also charged him for several other bombings as long ago as 2007 for which Wattana took responsibility. No one was killed in any of them. Wattana was charged for four bomb attacks and for unauthorized possession of weapons and explosives.

"I had no intention of causing any harm. I want to deeply apologize for the actions that caused injuries both severe and minor. I really want to apologize," Wattana said. He called the bomb he used "a giant firecracker." ..."